Speaker cabinet enclosure and method of tuning thereof

ABSTRACT

A speaker enclosure comprising a rectangular parallelepiped, main and auxiliary resonating chambers therein, a speaker unit mounted in the front wall of the enclosure forming the main resonating chamber, the chambers being separated by a baffle plate; tuned ports are disposed in the baffle plate adjacent the rear wall of the enclosure, these tuned ports providing communication between such chambers; tuned ports disposed in the front wall of the enclosure providing for communication of the auxiliary chamber with the exterior of the enclosure. Layers of insulation are provided within the cabinet enclosure as shown and described. The number, size, distribution and configuration of the indicated ports provide for faithful and clear reproduction of sound.

United States Patent Armstrong [54] SPEAKER CABINET ENCLOSURE AND METHOD OF TUNING THEREOF [72] Inventor: James C. Armstrong, 4017 Springrock Drive, Colerain Township, Hamilton County, Ohio 45239 [22] Filed: May 3, 1968 [21] Appl. No.: 726,517

[52] US. Cl. ..-....l8l/31 B [51] Int. Cl ..Gl0k 13/00, H04r H28 [58] Field ofSearch ..l81/3l,3l.l

[56] References Cited UNITED STATES PATENTS 1,837,755 12/1931 Carlisle et al ..181/31 1,884,724 10/1932 Keller ..l81/31 2,766,839 10/1956 Baruch et al. ..l8l/3l 3,131,783 5/1964 Mares ..l8l/31 3,239,028 3/1966 Murray ..181/31 3,360,073 12/1967 Murry ..l8l/31 51 Oct. 10, 1972 Primary Examiner-Stephen J. Tomsky AttorneyFrank L. Zugelter [57] ABSTRACT A speaker enclosure comprising a rectangular parallelepiped, main and auxiliary resonating chambers therein, a speaker unit mounted in the front wall of the enclosure forming the main resonating chamber, the chambers being separated by a baffle plate; tuned ports are disposed in the baffle plate adjacent the rear wall of the enclosure, these tuned ports providing communication between such chambers; tuned ports disposed in the front wall of the enclosure providing for communication of the auxiliary chamber with the exterior of the enclosure. Layers of insulation are provided within the cabinet enclosure as shown and described. The number, size, distribution and configuration of the indicated ports provide for faithful and clear reproduction of sound.

6 Claims, 14 Drawing Figures BACKGROUND OF THE INVENTION 1 Field of the Invention The field of art to which the invention is most likely to pertain is generally located in the class of apparatus relating to speakers. Class 181, Acoustics, United States Patent Office Classification, appears to be the applicable area of art in which the claimed subject matter of the type involved here has been classified in the past.

2. Description of the Prior Art Loudspeaker apparatuses, of the type involved here,

are disclosed in US. patents classified in said Class 181.

SUMMARY A still further object of his invention is to provide for a novel method of establishing clear and faithful reproduction of sound from a cabinet enclosure.

Another object of this invention is to provide for a novel method of tuning novel combinations of ports in a speaker enclosure whereby clear and faithful reproduction os sound is achieved.

Another important object of this invention is to extend the usable range of frequencies of a full range speaker unit in an enclosure and by which an over-all, flatter response is obtained without any adverse effect.

This invention is a patentable improvement over my previous disclosures as shown in my U.S. Letters Pat. No. 3,412,824 issued Nov. 26, 1968., and my subsequently filed patent application, Ser. No. 684,724, filed Nov. 21, 1967. In this particular reduction to practice, I again am able to achieve the object of obtaining evenness in backloading of the speaker cone thereby extending the over-all frequency range, and power handling range, which, to my knowledge, has never been taught or suggested in the prior art until shown by these disclosures, in addition to providing for clear and faithful reproduction of sound.

Another object of my invention resulting from even backloading of the speaker cone is an increase in the power handling capabilities of the speaker unit.

These and other objects and advantages of this invention will become more apparent by a full reading of the following description, claims appended thereto, and drawing comprising two sheets.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a perspective view, partially broken away, of a cabinet embodying my invention.

FIG. 2 is a view taken on line 2-2 of FIG. 1.

FIG. 3 is an elevational view of the front wall of the cabinet shown in FIG. 1.

FIG. 4 is a view taken on line 4-4 of FIG. 1.

FIG. 5 is a view taken on line 55 of FIG. 1.

FIGS. 6 through 13 are fragmentary views of structure in which modified port configurations, distributions and arrangements are utilized in the invention.

FIG. 14 is a schematic diagram showing increasing volume as a function of increasing frequency for a given speaker unit.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing in which reference characters correspond to like numerals in the following description, 20 (FIG. 1) represents generally a speaker cabinet enclosure embodying my invention. Enclosure 20 comprises a cabinet 22 of rectangular parallelepiped construction. Cabinet 22 comprises a pair of opposing spaced side walls 24, 26, a front wall 28, a rear wall 30, a top wall 32, and a bottom or base wall 34. Cabinet 22 is formed from thin boards, plywood, or other suitable material known for its utility in the production of speaker enclosure cabinets. The edges of the side walls 24, 26, top wall 32, and base wall 34 are recessed as at 36 (FIGS. 1, 2 and 4) along their vertically and horizontally disposed edges, as the case may be, so as to produce shoulders against which front and rear walls 28, 30 abut upon assembly of cabinet 22, thereby providing for a flush juncture of the exterior faces of walls 28, 30, with the faces of side walls 24, 26, top wall 32, and base 34. An airtight cabinet results from such assembly. A grille cloth (not shown) may be mounted upon wall 28 and molding (not shown) applied to the front wall thereafter for providing an artistic or stylish appearance to cabinet 22 as a whole.

A wooden bar or strip 40 (FIGS. 4, 5) or the like is mounted along each interior juncture of top and bottom walls 32, 34 with side walls 24 and 26. Means 41, such as nails, secure each of bars 40 to walls 24, 26, 32, 34, as the case may be. Means, such as a plurality of screw holes, are provided in rear wall 30 for registering upon the aforementioned shoulders whereby wood screws (not shown) secure rear wall 30 to the side, top and base walls of cabinet 22. Means 43, such as ring shank nails (FIGS. 1, 3), tack and secure front wall 28 to such walls. Glue is used in combination with means 41, 43.

A baffle plate 44 is mounted within cabinet 22 whereby a main resonating chamber 45 is formed and separated from a smaller auxiliary resonating chamber 46 of cabinet enclosure 20. As shown in FIGS. 1, 4, baffle plate 44 is dovetailed into the front, rear and side walls of cabinet 22, in generally parallel fashion to top and base walls 32, 34, by means of a groove 47 in each of such walls, thereby sealing off the chambers 45, 46 from each other. A plurality of screws 48 secure baffle plate 44 to front and rear walls 28, 30, as illustratively shown in FIGS. 1 and 3 with respect to front wall 28.

A layer of insulation 50, such as fiberglass, is mounted against the interior face of each of side walls 24, 26 forming both resonating chambers 45, 56, as shown in FIGS. 1, 4 and 5, and upon base wall 34. An insulation layer 50 is mounted to each face of baffle plate 44 (FIG. 4). It should be noted that the layers of insulation 50 across apertures 54 disposed in baffle plate 44, hereinafter more fully described, do not adversely affect nor significantly weaken the excellent results in faithful reproduction'of sound obtained in the layer 50 need not cover apertures 54. The air at these apertures 54 is sufficiently compressed to overcome any significant negative effect that may be produced by such layers thereover. However, assembly of cabinet 22 is facilitated by not including the step of cutting out portions of an insulation layer that covers such apertures 54.

A layer of insulation 50 is also securely mounted to the underside of top wall 32. No insulation is mounted to the interior face of front wall 28 forming either chamber 45 or 46. An insulation layer (not shown) may be optionally mounted to the interior face of the portions of rear wall 30 forming main and auxiliary chambers 45, 46.

One or more insulation layers 56, substantially co-extensively in width and height of main chamber 45, is disposed between the rear of speaker unit 52 and the positioning of apertures 54, preferably immediately abutting the rear of speaker unit 52 as shown in FIG. 4.

A full range speaker unit 52 is supported and secured to the interior face of front wall 28 forming chamber 45 by suitable means, such as screws 58 provided in such front wall 28 about an opening 60 therein. The positioning of speaker unit 52 about opening 60 and upon front wall 28 is obtained in the following manner: the axis of speaker unit 52 is so located with respect to front wall 28, and thus main chamber 45, that each of our linear distances a, b, c, d, measured, as shown in FIG. 3, along the major and minor axes of the frame of speaker unit 52, between a point on the periphery of the frame to its corresponding side wall, base wall or baffle plate, is co-equal with the other such linear distances, the respective directions of measurement being perpendicular to the corresponding side wall, base wall and baffle plate, as the case may be. In this manner, the speaker unit 52 and its cone are centrally mounted on front wall 28 in main chamber 45 with respect to the side and base walls and baffle plate of cabinet 22. Thus a round speaker as well as the oval speaker shown may also be utilized in the invention to achieve evenness of backloading on the cone of speaker unit 52.

Folded or doubled-over layers of insulation 62 are disposed in main resonating chamber 45, as shown in FIG. 5. These layers 62 are vertically aligned in such chamber and disposed generally parallel to side walls 24, 26 with their respective folds engaging insulation 50 on side walls 24, 26 and the frame of speaker unit 52.

As shown in FIGS. 1 and 2, a circular aperture 64 and a series of interconnected circular apertures 66 separated from aperture 64, and generally shown by reference character 54, are provided in baffle plate 64 adjacent rear wall 30 of cabinet 22. Their centers are disposed upon a line generally parallel to wall 30. As shown in FIG. 3, a plurality of series of interconnected circular openings 68, 70 is provided in that portion of front wall 28 forming auxiliary resonating chamber 46. The centers of openings 68, 70 generally lie on a line parallel with the plane of baffle plate 44. These apertures and openings 54, 68, and 70, constitute tuning ports and are tuned with respect to each other whereby the best overall flat response is obtained for enclosure 20 including desirable frequencies, described hereinafter, propagating from main resonating chamber 45 into auxiliary resonating chamber 46 through the position and configuration of the ports 64, 66 and ultimately through the position and configuration of the ports 68, 70 in front wall 28 of cabinet 22 to the exterior thereof.

A description of the method and principles utilized for tuning cabinet 20 now follows for a fuller understanding of the construction and operating of enclosure 20. To effect the method for tuning enclosure 20, we initially begin with ports 54, hereinafter sometimes referred to as the rear ports, and 68 and 70, hereinafter sometimes referred to as the front ports, having a total spatial area larger than what is ultimately achieved through tuning. This initial total spatial area is established or determined on the basis of state of the art knowledge of the relationship of cabinet volumes and free air resonance characteristics for given speaker units. Substantially no further change is then made in the value of the total spatial area for the rear and front ports. In the succeeding steps, change is made in the distribution, configuration and arrangement of the indicated front and rear ports; there may be a possibleincrease in the spatial area of the front port.

Cabinets A and B are first constructed in accordance with the above description, the assembly thereof being evident therefrom. Such change for the rear and front ports is made in accordance with the resonance length theory as applied to distribution, arrangement and configuration of ports in order to achieve optimum effectiveness in obtaining clear and faithful reproduction, and for flatness and extension of the response curve (FIG. 14) for enclosure 20. This theory is now described, with the accompanying five sketches illustrated below, as it applies to enclosure 20.

The higher frequencies resonate through longer lengths of an opening and/orseries of interconnected openings while the lower frequencies resonate through the shorter lengths of such an opening and/or series of interconnected openings.

Referring now to the sketches below:

sketch no. I

red line dio.=higher lowfrequenctes [H ii} red line dic.= lower low frequencies sketch no. 2

I reen lines mld run a frequencIes I I! sketch no.3

x: x 5; emphcsls on V g :E :i-wi high rmd range frequencles I r I l w I sketch no. 4

blue lines low high frequencies skeich no.5

emphasis on high high frequencies nected openings through which mid-range frequencies are able to propagate therethrough. These mid-range frequencies are represented by families of lines shown in green color, longer than the red lines (low frequencies), extending between any two adjoining interconnected openings (sketches 2 and 3) or between any three adjoining interconnected openings (sketch 3). Longer green lines represent and emphasize the high mid-range frequencies, as suggested by the legend accompanying sketch 3. Each sketch 4 and 5 illustrates a series of interconnected openings through which high frequencies are able to propagate therethrough. These high frequencies are represented by families of lines shown in blue color (being the longest lines illustrated) and extending between any four adjoining interconnected openings (sketches 4 and 5) or between any five adjoining interconnected openings (sketch 5). The longest blue lines represent and emphasize the high high frequencies, as suggested by the legend accompanying sketch 5.

On first blush, it may appear that the series of interconnected openings in baffle plate 44 and front wall 28,

7 exemplified by elements 66, 68, 70 and those shown in FIGS. 6 through 13, are simply or merely a single opening or an opening or variations thereof. However, in reality, such is not the case, in view of the theory described above for carrying out the practice of the invention. The distinguishing physical feature in each series of interconnected openings over an opening or single opening is that the perimeter of the wall structure forming each such series is not a geometrical continuously single closed curve, such as defines a circle or oval. Such perimeter is not a series of geometrical straight lines joining one another to form a traditionally-considered closed geometrical shape such as a rectangle, square, triangle, or other traditional closed polygonal shape. Rather, a repeating pattern of intersecting geometrical straight lines or curves is required to form each series of interconnected openings to provide definite physical restrictions on the lengths of the various frequency lines used in the resonance length theory by which the structure of the cabinet enclosure is fabricated, and such pattern constitutes the general wall perimeter of each such series. It should now be apparent that each series of interconnected openings as disclosed can not be defined as a single opening, and as exemplified by the FIGURES in the drawing is not formed in the same manner as an ordinary opening is.

Thus, in carrying out the method, taking sketch No. 2 for example, in applying the resonance length theory, each red line (representing a low frequency) in the interconnecting two circular openings is restricted to one of the interconnecting openings in each series, although red lines are found throughout the entire series. Each green line, however, representing mid-range frequencies, is not limited to a single one of the interconnecting openings in each series, but extend throughout the two (or more) interconnected openings. It should now be clear that the configuration of each opening in each series cannot be such so as to make the red and green lines substantially the same length, as then the resonance-length has no real significance toward achieving the objects of faithful and clear reproduction of sound. In other words, a singular circular or oval opening, or a single square, rectangular, triangular or traditionally-shaped polygonal opening can not constitute or define a series of interconnected openings as required in the practice of this invention.

The baffle plates and front walls of cabinets A and B are each first provided, as a matter of practicality, with a series of interconnected apertures and openings, the total spatial area thereof being greater than that required for normal tuning of both rear and front ports. The excess spatial area in the rear ports and in the front ports is eliminated by positioning corks or other appropriately shaped elements, in the excess number of the interconnected apertures and openings in such ports. The position of the corks in the front ports of cabinets A and B are made identical. The position of the corks in the rear ports of cabinets A and B are different. The initial choice of the positions of the corks in the rear ports of both cabinets is generally based upon the valleys (deficiencies) and peaks (excesses) of he frequency response curve for a given speaker unit (FIG. 14). FIG. 14 is representative of such a curve for the type of speaker units utilized in connection with the invention. Curve F represents the original frequency response curve of a speaker unit 22 for enclosure 20, i.e., for frequencies propagated in the forward direction of the cone of speaker unit 52 and for the unaltered frequencies propagated to the rear of such cone. Curve R represents the frequency response curve desired to be propagated from the rear of the cone of speaker unit 52 through cabinet 22. It is to be remem bered that it is these rearwardly propagated frequencies which, by this invention, are controlled by the positions of tuning ports 54 and 68, 70. Curve S represents the resultant frequency response curve, or the average of curves F and R, obtained in and for enclosure 20 by the tuning method being herein described. The distinct advantage achieved here is a flatter over-all frequency response curve S and extension of frequency responses into the extreme low and high frequencies resulting from this tuning method.

Where a valley (deficiency) exists on curve F, the frequencies in the range of the valley pass through the rear port. Where a peak (excess) exists, the frequencies permitted to propagate in the range of the peak are to be reduced. If a deficiency is in the very low frequencies, then few long series, if any, of interconnected openings are required; a plurality of singular openings may be the answer. The converse is true if deficiencies are in the higher frequencies. If both high and low frequencies are deficient for a given speaker unit, then a particular arrangement and distribution involving a combination of singular openings, series of interconrangement and distribution of rear ports are obtained.

Then the position of the corks in the rear ports of both cabinets A and B are made identical. This method of tuning is then repeated upon the front ports in cabinets A and B until the optimum arrangement and distribution of the front ports in one of the cabinets are obtained.

The initial choice of a size for an opening or series of interconnected openings to be incorporated into baffle plate 44 and front wall 28 is generally determined by the need for propagation of bass or low frequencies. The greater the need is, for low frequencies, the smaller the diameter of other comparable parameter for other geometrical configurations. Some trial and error may result to one unskilled, as to such an initial choice, however, this may be expected. But nevertheless, same is readily solved by quick experience.

In using the resonance length theory, although each addition of an opening to a series of interconnected openings carries with it the propagation of low or lower frequencies, nevertheless, control of the propagation and emphasis on chosen mid-range, high and higher frequencies is accomplished.

It should now be apparent that control of propagation of low, mid-range and high frequencies through tuning ports 54 and 68, 70 is obtained for enclosure 20 by determining the number of openings in a series of interconnected openings and the number of singular openings for such tuning ports in various distributions, and combinations or arrangements.

FIGS. 6 through illustrate other various arrangements and distributions of combinations of apertures 01' openings in baffle plate 44 or front wall 28 which may develop in the tuning of a given cabinet and speaker unit. FIG. 6 represents an arrangement of the combination of a singular opening and a series of interconnected openings. FIG. 7 represents an arrangement of a series of interconnected openings. FIG. 8 represents an arrangement of a plurality of singular openings. FIG. 9 represents an arrangement of the combination of a plurality of singular openings and plurality of a series of interconnected openings. FIG. 10 represents an arrangement of a combination of a singular opening and a plurality of series of interconnected openings.

FIGS. 11 through 13 illustrate that the nature of the openings for the tuning ports is not limited to a circular configuration, but includes other geometrical configurations such as triangles, ovals, rectangles and squares, and the like.

The enclosure 20 shown in FIGS. 1-3, embodying my invention, has the following characteristics:

Outside dimensions: 1 1 7/32 in. wide 18 23/32 in. high 1 H6 in. deep Material: plywood Wall thickness: )6 in.

Bnfllc plate 44 dimensions: A in. thick 10 31/32 in. wide 10 19/32 in. long (depth) Ports: front and rear: rear ports (FIG. 2):

l in. diameter holes 5 required, one spaced from 4 interconnected openings; their center line l b" from back edge of plate 44; center of first opening of interconnected openings 3% from side edge of plate, with center of all 4 interconnected openings being apart from each other in direction towards center of plate; the spaced opening being 1% from center of nearest opening in interconnected series.

7 required, 2 interconnected and spaced from 5 interconnected, openings; their center lines 2% in. from top edge of front wall 28; centers of 2 interconnected openings being 2% in. and 3% in. from side edge of wall;

center of first of 5 interconnected openings being 1% in. from center of last 2 interconnected openings;

is in. separating centers of 5 interconnected openings.

front port (FIG. 3):

manufactured by Oaktron Industries, Inc., Monroe, Wisconsin.

The spatial area for front port or ports 68, is, generally speaking, greater than the spatial area of rear port or ports 54, as a result of the construction of enclosure 20 and tuning thereof by the heretofore described method, as shown in FIGS. 1-3.

In operation of enclosure 20, the lead wires (not shown) connected in conventional fashion to speaker unit 52 are connected to a program source such as an amplifier, tape recorder, or the like, in a customary manner, and does not constitute a part of this invention. Such wires are preferably drawn through rear wall 30 for easy accessibility thereto.

Pursuant to the requirements of the patent statutes, the principle of this invention has been explained and exemplified in a manner so that it can be readily practiced by those skilled in the art to which it pertains, or with which it is most nearly connected, such exemplification including what is presently considered to represent the best embodiment of the invention. However, it should be clearly understood that the above description and illustrations are not intended to unduly limit the scope of the appended claims, but that therefrom the invention may be practiced otherwise than as specifically described and exemplified herein,

by those skilled in the art, and having the benefit of this disclosure.

Therefore, whatl claim as patentably novel is:

1. In a loudspeaker system formed by an enclosure cabinet of a parallele-piped construction including two pairs of spaced opposing parallel walls,

a main resonating chamber,

an auxiliary resonating chamber,

a speaker unit mounted in a front one of said walls and communicating with said main resonating chamber,

a baffle plate mounted interiorly of said parallel walls and sealing and separating said chambers from each other,

a first tuning port means in the rear of said baffle plate providing communication between said chambers, and

a second tuning port means in the portion of the front wall forming the auxiliary resonating chamber and communicating with the exterior of said cabinet enclosure,

the improvement comprising,

at least one series of interconnected openings mounted in said baffle plate and having a wall 10 connected openings thereby forming each said series of interconnected openings,

each said series of interconnected openings being distributed in their respective elements for providing a flat frequency response and extension of the frequency range for faithful reproduction of sound from said enclosure 2. The improvement of claim 1 in which a singular opening and a series of interconnected openings constitute said first tuning port means and a plurality of series of interconnected openings constitute said second tuning port means.

3. The improvement of claim 1 in which the combination of a singular opening with a series of interconnected openings constitutes each said first and second tuning port means.

4. The improvement of claim 1 including a series of interconnected openings constituting each said first and second tuning port means.

rather such formed arrangement repeating a pattern of crossing straight lines or curves between contiguous openings in each said series of inter- 5. The improvement of claim 1 in which the combination of a plurality of singular openings and a plurality of a series of interconnected openings constitute each said first and second tuning port means.

6. The improvement of claim 1 in which the combination of a singular opening and a plurality of series of interconnected openings constitute each said first and second tuning port means.

* t t l 

1. In a loudspeaker system formed by an enclosure cabinet of a parallele-piped construction including two pairs of spaced opposing parallel walls, a main resonating chamber, an auxiliary resonating chamber, a speaker unit mounted in a front one of said walls and communicating with said main resonating chamber, a baffle plate mounted interiorly of said parallel walls and sealing and separating said chambers from each other, a first tuning port means in the rear of said baffle plate providing communication between said chambers, and a second tuning port means in the portion of the front wall forming the auxiliary resonating chamber and communicating with the exterior of said cabinet enclosure, the improvement comprising, at least one series of interconnected openings mounted in said baffle plate and having a wall perimeter forming a portion of said first tuning port means therein and disposed adjacent a wall opposing the front wall of said cabinet, at least one series of interconnected openings mounted in the portion of the front wall forming said auxiliary resonating chamber and having a wall perimeter forming a portion of said second tuning port means, said wall perimeter for each said one series of interconnected openings not forming a geometrical arrangement by which a single traditional polygonal-shaped opening such as an oval, circle, square, rectangle, triangle or the like is established, but rather such formed arrangement repeating a pattern of crossing straight lines or curves between contiguous openings in each said series of interconnected openings thereby forming each said series of interconnected openings, each said series of interconnected openings being distributed in their respective elements for providing a flat frequency response and extension of the frequency range for faithful reproduction of sound from said enclosure
 2. The improvement of claim 1 in which a singular opening and a series of interconnected openings constitute said first tuning port means and a plurality of series of interconnected openings constitute said second tuning port means.
 3. The improvement of claim 1 in which the combination of a singular opening with a series of interconnected openings constitutes each saId first and second tuning port means.
 4. The improvement of claim 1 including a series of interconnected openings constituting each said first and second tuning port means.
 5. The improvement of claim 1 in which the combination of a plurality of singular openings and a plurality of a series of interconnected openings constitute each said first and second tuning port means.
 6. The improvement of claim 1 in which the combination of a singular opening and a plurality of series of interconnected openings constitute each said first and second tuning port means. 